A duplex communication system is one that supports point-to-point communication between two parties in both directions. In a full-duplex (FD) communication system, the communication may occur in both directions at the same time, and in a half-duplex (HD) communication system, the communication may occur in only one direction at a time.
FD and HD operations are typically implemented using either time-division duplexing (TDD) or frequency division duplexing (FDD). In TDD, outward and return signals are communicated on the same carrier frequency, but at different times (e.g., in different time slots or non-overlapping subframes). In FDD, outward and return signals are communicated on different carrier frequencies, and can be communicated at the same or different times. In full-duplex FDD (FD-FDD) outward and return signals are communicated at the same time, and in half-duplex FDD (HD-FDD), outward and return signals are communicated at different times.
The Long-Term Evolution (LTE) standard provides for both TDD and FDD modes of communication, with the FDD mode being either an FD-FDD mode or an HD-FDD mode. The HD-FDD mode has the potential benefit, under certain frequency arrangements, of being implemented without a duplex filter. For instance, a device implementing HD-FDD may use a switch to change between different frequency channels rather than using a duplex filter to maintain concurrent communication on two different frequency channels. The omission of a duplex filter may allow such a device to be implemented at relatively lower cost and with lower power consumption compared to devices that require a duplex filter. Accordingly, the use of HD-FDD may be particularly attractive for certain low-cost applications.
Some envisioned uses of the HD-FDD mode include various forms of machine type communication (MTC). MTC communication generally involves communication between machines and other machines (e.g., machine-to-machine communication) and/or between machines and humans. Such communication may include, for example, the exchange of measurement data, control signals, and configuration information. The machines involved in MTC may be of various forms and sizes, ranging from wallet-sized devices to base stations, for example. An example low-cost application of MTC is telemetry, e.g., remote temperature sensing, meter reading, and so on. In many such applications, MTC devices are deployed in large numbers, with each device operating in infrequent bursts. Accordingly, it may be beneficial to reduce the cost and/or power consumption of each device by omitting a duplex circuit and relying on HD-FDD communication.
In certain contexts, such as LTE based systems, HD-FDD communication may occur between one or more devices that support HD-FDD but not FD-FDD communication (hereafter, an “HD-FDD device”), and one or more other devices that support both HD-FDD and FD-FDD communication (hereafter, an “FD-FDD device”). In such contexts, a scheduler in an FD-FDD device (e.g., an eNodeB) may be required to consider data and control traffic in both directions when making scheduling decisions for an HD-FDD device (e.g., a low-cost MTC device). This requirement tends to add complexity to the scheduler. For example, when not in discontinuous receive (DRX) mode, the HD-FDD device may continuously receive information through downlink physical channels except when instructed by the network to transmit in the uplink or when transmitting through the physical random access channel (PRACH) on an unscheduled basis (e.g., contention-based). A switching time will need to be observed by HD-FDD devices when transitioning from receive to transmit and vice versa, and this switching time will need to be taken into account by the scheduler.
HD-FDD operation is generally implemented as a scheduler constraint, implying that the scheduler ensures that an HD-FDD device is not scheduled simultaneously in the downlink (DL) and uplink (UL). There are occasions where DL and UL transmissions cannot be avoided by scheduler constraints, such as where an HD-FDD device transmits through the PRACH on an unscheduled basis (contention-based) that cannot be predicted by an eNodeB (eNB). For example, it is possible that the HD-FDD device may transmit through the PRACH in the UL at the same time that it is scheduled to transmit through the physical downlink control channel (PDCCH) or physical downlink shared channel (PDSCH) in the DL. Under these circumstances the HD-FDD device will not be able to receive through the PDCCH/PDSCH.
The following issues have been further observed with respect to switching times of HD-FDD devices. First, a switching time for a DL-to-UL transition may be created by allowing the HD-FDD device to DRX the last orthogonal frequency division multiplexing (OFDM) symbols in a downlink subframe immediately preceding an uplink subframe. Second, a switching time for a UL-to-DL transition may be created by setting an appropriate amount of timing advance in the HD-FDD device. This switching time may be particularly beneficial where the HD-FDD is close to a cell center (with near zero timing advance). The same adjustment of the uplink timing from an eNB perspective is also applied to FD-FDD user equipment (UE).
Radio measurements done by UE (either HD-FDD or FD-FDD devices) are typically performed on both serving cells and neighbor cells over some known reference symbols or pilot sequences. Such measurements can be done on cells on an intra-frequency carrier, inter-frequency carrier(s) as well as on inter-radio-access-technology (inter-RAT) carriers(s) (depending upon the UE capability, whether it supports that RAT). To enable inter-frequency and inter-RAT measurements for a UE requiring measurement gaps, the network must configure the measurement gaps. Two periodic measurement gap patterns both with a measurement gap length of 6 ms are defined for LTE. Some measurements may also require the UE to measure signals transmitted by the UE in the UL.
Measurements can be performed for various purposes. Some example purposes include mobility, positioning, self-organizing network (SON), minimization of drive tests (MDT), operation and maintenance (O&M), and network planning and optimization. These and other types of measurements are typically performed over longer time durations on the order of few 100 ms up to several seconds.
The same measurements are generally applicable in single carrier and carrier aggregation (CA), although in CA, measurement requirements may be different. For example, a measurement period may be different in CA—it may be either relaxed or more stringent depending upon whether a secondary component carrier (SCC) is activated. This may also depend on the UE capability, i.e. whether a CA capable UE is able to perform measurement on SCC with or without gaps.
UE mobility measurements in LTE may include, for example, physical cell identity (PCI) acquisition measurements, reference symbol received power (RSRP) measurements, reference symbol received quality (RSRQ) measurements, and cell global identity (CGI) acquisition measurements, among others. Mobility measurements may also include measurements for identifying or detecting cells belonging to various different types of systems, such as LTE, high speed packet access (HSPA), CDMA2000, global system for mobile communications (GSM). The cell detection typically comprises at least PCI acquisition and subsequent signal measurement(s) (e.g. RSRP) of a target cell. The UE may also have to acquire the CGI of a UE. More specifically the US may read system information (SI) to acquire the CGI of the target cell. The UE may also acquire other information from the target cell, such as a closed subscriber group (CSG) indicator, or CSG proximity indicator.
UE positioning measurements in LTE may include, for example, reference signal time difference (RSTD) measurements and UE receive-transmit (RX-TX) time difference measurements. UE RX-TX time difference measurements require the UE to perform measurement on DL reference signals as well as on UL transmitted signals.
UE measurements for radio link maintenance, MDT, SON, and other purposes may include, for example, control channel failure rate or quality estimates (e.g., paging channel failure rate measurements, broadcast channel failure rate measurements), and physical layer problem detection (e.g. out of synchronization [out of sync] detection, in synchronization [in-sync] detection, radio link monitoring, and radio link failure determination or monitoring).
UE measurements of channel state information (CSI) may be used for scheduling and link adaptation by a network, for example. Examples of such CSI measurements include, for example, channel quality indicator (CQI) measurements, precoding matrix index (PMI) measurements, and rank indicator (RI) measurements. These measurements may be performed with respect to reference signals such as a cell-specific reference signal (CRS), a CSI reference signal (CSI-RS), or a demodulation reference signal (DMRS).
Radio measurements performed by the UE can be used by the UE for one or more radio operational tasks. Examples of such tasks include reporting measurements to the network, which in turn may use them for various tasks. For example, in a radio resource control (RRC) connected state, the UE reports radio measurements to a serving network node. In response to the reported UE measurements, the serving network node takes certain decisions e.g. it may send a mobility command to the UE for a cell change, such as a handover, RRC connection re-establishment, RRC connection release with redirection, primary cell (PCell) change in CA, policy and charging control (PCC) change in PCC, for example. In an idle or low activity state, an example of cell change is cell reselection. In another example, the UE may itself use radio measurements for performing tasks, such as cell selection or cell reselection, for example.
Similar to a UE, a radio network node (e.g., an eNB) may also perform various types of measurements to support related functions, such as mobility (e.g. cell selection, handover, etc.), positioning a UE, link adaption, scheduling, load balancing, admission control, interference management, interference mitigation. These measurements are generally performed on signals transmitted and/or received by the radio network node, and may include, for example, signal-to-noise ratio (SNR), signal-to-interference-plus-noise ratio (SINR), received interference power (RIP), block error rate (BLER), propagation delay between UE and the radio network node, transmit carrier power, transmit power of specific signals (e.g. TX power of reference signals), and positioning measurements.